A data center (DC) side virtual private network (e.g., Ethernet VPN-EVPN) overlay and the data center interconnect (DCI) side wide area network (WAN) (e.g., a L2VPN/L3VPN) control plane may or may not be within the same administrative domain. This implies that a single router target (RT) namespace across these multiple administrative domains cannot be guaranteed. A DC side address family may or may not be the same as a DCI side address family.
Border Gateway Protocol (BGP) is a routing protocol of the Internet that maintains a table of IP addresses (i.e., prefixes) which designate network reachability among autonomous systems (AS's). As used herein, an AS is a connected group of one or more IP prefixes run by one or more network operators which has a single and clearly defined routing policy. As used herein, the term “BGP” refers to all forms of BGP, including internal-BGP and external-BGP. Each BGP advertised route must be unique, otherwise, a subsequent advertisement of the route will consider it the same, and overwrite any previous information received about the route. BGP extensions advertise routes for a Virtual Private Network (VPN). A VPN-IPv4 address is a 12-byte string, beginning with an 8-byte Route Distinguisher (RD) and ending with a 4-byte IPv4 address. If several VPNs use the same IPv4 address prefix, these will be translated into unique VPN-IPv4 address prefixes, making it possible for BGP to carry several completely different routes to that IP address.